With large-scale application of Internet Protocol (IP) technology and IP networks in telecommunication field, telecommunication services are packetized gradually, such that more value-added services, especially multimedia services, may be provided over packet-based IP networks. At present, IP networks mainly bear Internet services which are best-effort services without strict demand on the Quality of Service (QoS).
The emergence of Next Generation Network (NGN) services puts forward a great challenge to the conventional best-effort Internet networks and technologies. Nowadays, NGN is a focus concerned and discussed by communication enterprises. People wish to provide solutions for issues in various networks such as network convergence, forward/backward-compatible smooth evolution, establishment of profitable business modes for adding Average Revenue Per User (ARPU), Average Profit Per User (APPU) and efficient multi-service added values by means of NGN. Conventional Internet networks and technologies may not provide telecom-level NGN services. More and more telecom organizations and operators believe that NGN should absorb the technologies of Internet, discard the idea of Internet, and refer more to the idea of Public Switched Telephone Network (PSTN) instead. The problems existing in NGN at present are mainly focused on QoS, security, protection, and signaling system, etc. The Service control plane of NGN is most frequently and maturely researched in NGN, and the practice of NGN has shown that the transport service of NGN has become one of the largest technological barriers to the development of NGN.
At present, International Telecommunications Union (ITU-T) divides NGN into a service layer and a transport layer, and each layer may be divided into a user plane, a control plane and a management plane. From the view of the practical network construction of NGN, the service layer of NGN includes various Application Layer devices, and the transport layer is generally composed of IP Routers and Ethernet Switchers, Asynchronous Transfer Mode (ATM), private-line direct interconnection and physical transport layer network; From the view of protocol hierarchy, the transport layer of NGN includes a physical transport sub-layer (L1) and a packet transport sub-layer (L2, L3-L7). This method shifts the processing and switching functions of IP Layer and the protocol layers above IP Layer (including L3-L7 of ISO network protocols) implemented by routers to the transport layer. With appearance of multi-service routers, more and more complicated features of NGN service layer will be implemented in routers, which will cause a confusion of the service layer and the transport layer when the NGN is physically implemented; for example, the multi-service routers in NGN implement not only many functions of the service layer but also functions of the transport layer, which is harmful to a simple, secure and low-cost construction of transport network of NGN, an finally harmful to the building of telecom-level NGN. Therefore, from the view of development, it is more reasonable to logically allocate the functions of IP Layer and the layers above IP layer (L3-L7) to the service layer of NGN, and the physical implementation of the service layer and the transport layer in NGN should be clearly separated.
The network technologies of the Physical Layer in NGN mainly include SDH technology and Optical Transport Network (OTN) technology, in which SDH technology has been very mature after many-year development. At present, the SDH technology is developed toward Multiple Service Provisioning Platform (MSPP); MSPP is a convergence of packet technology and SDH technology; besides Ethernet interface and the layer 2 (L2) switching, ATM interface and ATM switching, MSPP also begins to support Resilient Packet Ring over SDH (RPR over SDH), Multi-Protocol Label Switching over SDH (MPLS over SDH); the enhancement of data characteristics in MSPP and the standardization of technologies such as Generic Framing Protocol (GFP), Link Capacity Adjustment Scheme (LCAS) and Virtual Concatenation make SDH networks possess stronger and stronger transport capability for NGN services. OTN is a development of Wavelength-Division Multiplexing (WDM) technology, which enables a wavelength-division network to have an ability of constructing telecom-level optical transport networks; at present ITU-T has substantially completed the standardization of the main contents of OTN; OTN implements large-granularity transport with bandwidth larger than 2.5G suitable for NGN broadband services, therefore it is one of the key network technologies for Physical Layer transport of NGN in the future.
As for the control plane of the transport layer, the control plane protocols of respective sub-layers of the transport layer are isolated from each other, and there is no strict separation between the control plane and the user plane; wherein the control protocol of MPLS of the packet transport sub-layer has been relatively mature. As for the control protocol of the physical transport sub-layer, the appearance of Automatically Switched Optical Network (ASON) technology makes it possible for the physical layer network to be controlled though signaling; nowadays ASON has been applied in a broader and broader range, which adopts a signaling protocol similar to the signaling protocol of MPLS; therefore from a long-term point of view, it is possible for the control protocol of MPLS sub-layer and the control protocol of ASON to be unified.
In the prior methods for implementing NGN, several methods may be used for implementing the user plane of the transport layer in NGN as follows:
(1) separating the packet transport sub-layer and the physical transport sub-layer: implementing the service layer and the MPLS Packet transport sublayer with routers, bearing them on the physical transport sublayer devices such as Synchronous Digital Hierarchy/Wavelength-Division Multiplexer/Optical Transport Network (SDH/WDM/OTN).
(2) adopting MSPP: MSPP is a convergence of packet technology and SDH technology. At present, the MSPPs of a part of manufacturers possess MPLS function, and their implementation of MPLS may be concluded as two modes:
One mode is to implement MPLS on the User Network Interface (UNI) Board of MSPP, as shown in FIG. 1; the MPLS data flows are directly mapped into SDH Virtual Containers (SDH VCs) through the UNI Interface Board, and then transferred to the SDH High Order/Low Order (SDH HO/LO) crossing.
The other mode is to design a centralized MPLS switching module, as shown in FIG. 2; the MPLS data flows accessing through the UNI are mapped into SDH VCs, and transferred into the centralized MPLS switching module through the SDH HO/LO crossing for switching; or the MPLS data flows from the SDH UNI (borne on SDH VCs) are crossed through the SDH HO/LO, and then transferred to the centralized MPLS switching module for switching.
The above-mentioned two modes mainly aim to transport private line services; both of them may not meet the demand of large-scale and large-capacity NGN service transport.
In summary, in the prior network architectures and implementation methods of NGN, the service layer and the transport layer of NGN are confused; for example, the service routers may implement not only many functions of the service layer but also the functions of the transport layer. The lack of independence of the transport layer control plane in NGN makes it difficult to establish a secure signaling plane. The separated implementation of the transport layer functions is unfavorable to the construction of telecom-level transport network with high-efficiency and high-availability, or the reduction of the cost of transport network.